STARRY SPLENDOR IN CORE OF OMEGA CENTAURI

The core of the spectacular globular cluster Omega
Centauri glitters with the combined light of 2 million
stars. The entire cluster contains 10 million stars,
and is among the biggest and most massive of some
200 globular clusters orbiting the Milky Way Galaxy.
Omega Centauri lies 17,000 light-years from Earth.

Astronomers Eva Noyola, of the Max-Planck Institute
of Extraterrestrial Physics in Garching, Germany,
and Karl Gebhardt of the University of Texas at
Austin, have reported on the possible detection
of an intermediate-mass black hole in the core of
Omega Centauri.

The result is primarily based on spectroscopic
measurements obtained with the Gemini South observatory
in Chile which suggest the stars are moving around
the central core of the cluster at higher than expected
velocities.

Among the possible explanations for these speedy
stars—and the one favored by their study—is
that an intermediate-mass black hole of approximately
40,000 solar masses resides at the center of Omega
Centauri. Its powerful gravitational field speeds
up the motions of stars near the core.

Astronomers have speculated for years that some
globular clusters may harbor in their centers medium-size,
or intermediate-mass, black holes with masses of
some tens of thousands of suns. Medium-size black
holes are much less massive than the supermassive
black holes, which are up to billions of solar masses
and reside in the centers of large galaxies.

Hubble images taken with the Advanced Camera for
Surveys were used in key areas in support of this
study: to help pinpoint the center of the cluster,
as well as to measure the amount of starlight at
the cluster center.

Using the European Southern Observatory’s
Very Large Telescope in Paranal, Chile, Noyola and
Gebhardt are planning to obtain follow-up observations
to help confirm the existence of an intermediate-mass
black hole.